The Supreme Court announced Friday afternoon that it will take up same-sex marriage, hearing both a case stemming from California’s Proposition 8 voter-approved ban on gay marriage and a case from New York challenging the constitutionality of the 1996 Defense of Marriage Act.

The pair of moves greatly increase the chances that the justices will rule this term on whether the U.S. Constitution guarantees same-sex couples the right to marry. However, it’s still possible the high court could dispose of both cases without squarely addressing that central issue.

A panel of the U.S. Court of Appeals for the 9th Circuit ruled 2-1 in February that the 2008 California ballot measure that banned gay marriage was unconstitutional because it stripped same-sex couples of a right to marry without adequate justification. The decision did not assert a right for gay couples to marry in states where such unions were never recognized.

The leader of a prominent group opposing same-sex marriage said the fact that at least four justices voted to take up the California case suggests the high court is poised to set aside the 9th Circuit ruling.

“We believe it is a strong signal that the Court will reverse the lower courts and uphold Proposition 8,” John Eastman of the National Organization for Marriage said in a statement. “That is the right outcome based on the law and based on the principle that voters hold the ultimate power over basic policy judgments and their decisions are entitled to respect.”

However, a key lawyer fighting to legalize gay marriage said Friday he expects the justices to rule in favor of same-sex couples seeking to marry.

“We are very confident the outcome of this case will be to support the rights of our gay and lesbian brothers and sisters,” former solicitor general Ted Olson told reporters on a conference call.

The other case the justices agreed to take up stems from estate taxes owed by a New York woman after the death of her longtime, female partner, whom she married in Canada. In October, a panel of the U.S. Court of Appeals for the 2nd Circuit issued a 2-1 ruling that collecting such taxes from same-sex spouses — but not from heterosexual married couples — violated the U.S. Constitution.

The uncertainty about whether the Supreme Court will ultimately grapple with the core issues in the cases springs from the justices’ instructions in Friday’s order. The justices told the lawyers in both cases to address whether the court can decide the central issues, given questions about the way the cases arrived at the court.

State officials in California, including former Gov. Arnold Schwarzenegger and current Gov. Jerry Brown, declined to defend the state constitutional amendment voters passed, 52 percent to 48 percent, in 2008. Lower courts allowed proponents of the ballot measure to defend it, but there have been lingering questions about their legal standing to do so.

The Defense of Marriage Act case raises a similar question, since President Barack Obama’s administration decided in 2011 not to defend the 1996 law. Leaders in the House of Representatives, acting through a congressional panel called the Bipartisan Legal Advisory Group, unsuccessfully took up the defense of DOMA and filed the petition the Supreme Court agreed to accept on Friday. It’s unclear whether congressional leaders have the right to defend the law, as lower courts permitted them to do.

“We think [the justices] will probably get to the merits, notwithstanding the standing issues,” Olson said.

Arguments are expected in the spring. Decisions in the cases are likely by the end of the court’s term in June.